In recent years, with rapid development of digital cameras, camera cell-phones and the like, a smaller-sized solid imaging device and a high resolution solid imaging device are required. Since miniaturization of the solid imaging device causes deterioration of sensitivity, light is collected efficiently to prevent the deterioration of device sensitivity by locating a collecting microlens between an optical sensor part and a color filter part or above the color filter part, by forming a white (transparent) color filter at a color filter part, or by forming an optical waveguide between an optical sensor part and a color filter part. Examples of a common production method of the collecting microlens, the white (transparent) color filter, or the optical waveguide include a method of processing, by dry etching, inorganic films formed by a CVD method or the like, and a method of applying and processing a resin. The former method is hard to achieve a refractive index of 1.65 to 2.00 which is most suitable for the collecting microlens, the white (transparent) color filter or the optical waveguide, and therefore the latter method receives attention. That is, a resin composition with high refractive index is required.
Heretofore, for example, a photosensitive siloxane composition containing a polysiloxane, a quinone diazide compound, a solvent and a thermally crosslinkable compound (see e.g., Patent Document 1), and a high refractive index material obtained from a composition containing a siloxane compound having an aromatic hydrocarbon group (see e.g., Patent Document 2) are proposed. However, it has been difficult that these materials provide a cured film having adequately high refractive index.
Further, a positive photosensitive resin composition containing polyamide acid, a compound having a phenolic hydroxyl group, a quinone diazide compound and inorganic particles (e.g., Patent Document 3), and a silicone copolymer which comprises silsesquioxane having a phenol unit and a condensed polycyclic hydrocarbon group (see e.g., Patent Document 4) are proposed. However, the photosensitive resin composition and copolymer have a problem that the transparency is deteriorated since the polyamide acid or the phenolic hydroxyl group is colored.
As a material which achieves high refractive index and high transparency simultaneously are disclosed a coating composition containing an organosilane, a siloxane oligomer and fine particles and/or sol of a metal oxide (e.g., Patent Document 5), and a siloxane-based resin composition formed by copolymerizing metal oxide particles with an alkoxysilane (see e.g., Patent Document 6). Since these materials are non-photosensitive, the compositions are usually processed by a wet etching method using chemicals or a dry etching method using plasma in forming a pattern.
Further, a siloxane-based resin composition having high refractive index and high transparency due to positive photosensitivity (see e.g., Patent Document 7) is proposed.